A workable purification scheme has been devised for the isolation of a large molecular weight form of rat insulin-like growth factor-II (IGF-II) also known as multiplication stimulating activity (MSA). Human fetal fibroblasts have been shown to produce at least two size classes of IGF's as well as an IGF binding protein. An IGF-II receptor purified from chondrosarcoma chondrocytes has been shown to be fully active and greater than 90% pure.